A 5kg sphere of 239Pu is initially unable to sustain a chain reaction because the effective multiplication factor is slightly below unity. If the sphere is rapidly compressed to half its original radius without any change in mass, which statement best describes the result?
(a) The multiplication factor is unchanged because mass remains the same
(b) The multiplication factor decreases further, making sustained reaction even less likely
(c) The multiplication factor increases and the assembly may reach or exceed criticality
(d) The chain reaction stops because higher density causes complete neutron absorption